ATHENS, Greece (AP) — A Greek militant anarchist group has claimed responsibility for a letter bomb sent to an anti-terrorism prosecutor, which exploded on Sunday without causing injury or damage.

The Conspiracy Nuclei of Fire, or SPF, is also urging other anarchists to attack members of the judiciary. It says it targeted Dimitris Mokkas in revenge for recent arrests over another letter bomb sent to a former police anti-terrorism chief.

In a posting on a leftist website Tuesday, the SPF said many judges lack police guards and are “easy to find.” It called for attacks ranging from bodily assault to bombings and “executions.”

The SPF is a self-described “anti-social” nihilist group behind a string of bombings since 2008, which claimed no victims. More than 20 suspected SPF members have been charged with terrorism.